Microstructure And Properties Of High-strength And Heat-resistant Al-Zr Alloy Prepared By Non-equilibrium Solidificatio

Al-Zr alloys are characterized by high temperature resistance,high strength and high current-carrying capacity,and are commonly used in high-capacity grid transmission.However,the low solid solution of Zr in the aluminum matrix（<0.28%,mass fraction,same below）during equilibrium solidification and the small fraction of second phase precipitated after aging limit the strength level of the alloy.In this paper,Al-Zr alloys were prepared by gas-assisted continuous casting and extrusion（GAC）non-equilibrium solidification technology.The cooling rate can reach10³-10⁴ K/s,and the solid solubility of Zr in the aluminum matrix was increased by at least 40.6%.The higher supersaturation is beneficial to improve the aging efficiency and precipitate the smaller Al₃Zr（L1₂）phase.In this paper,the microstructure and properties of Al-Zr alloy were studied.The main conclusions are as follows:（1）Compared with the as-cast state,the GAC process not only enhances the solid solution degree of Zr in the aluminum matrix,but also significantly refines the grain size of the aluminum matrix,while significantly changing the morphology,size and dispersion state of the primary phase.（2）The Zr content has a strong influence on the organizational properties of the GAC state alloy.Grain size is inversely proportional to the Zr content solidly dissolved in theα-Al matrix.The electrical conductivity decreases with increasing Zr content and the strength increases with increasing Zr content,but when the solid solution of Zr in theα-Al matrix reaches the upper limit,the decrease in electrical conductivity and the increase in strength are not obvious.（3）During the aging process of Al-Zr alloy,the supersaturated solid solution decomposes and forms a large number of sub-stable A1₃Zr（L1₂）phases that co-lattice with the matrix,and more A1₃Zr（L1₂）phases are precipitated away from the primary phase.The multi-step isochronal aging is more efficient,but the performance is not good;isothermal aging can obtain excellent overall performance,but the efficiency is low;multi-step aging can obtain excellent mechanical properties,but it is not good for the improvement of electrical conductivity.（4）The effects of isothermal aging and cold deformation synergistic treatment of Al-0.80Zr（φ10mm）alloy on the tissue properties are discussed.The best performance is achieved by isothermal aging+drawing treatment,where the matrix grains are refined to submicron size at 94%deformation,and high density dislocations and lamellar dislocations are formed inside the grains/subgrains;the tensile strength can reach 278.0 MPa,which is significantly higher than the reported strength level of Al-Zr-based wires.Calculated results show that the main strengthening mechanisms are precipitation phase strengthening,grain boundary strengthening and dislocation strengthening.（5）The effects of the Al-1.0Zr（φ10 mm）alloy treated synergistically by cold deformation and isothermal aging on the tissue properties are discussed.The best performance of ECAP-Conform+isothermal aging treatment was achieved with57.27%IACS and 204.4 MPa for electrical conductivity and tensile strength,respectively.it is worth noting that ECAP-Conform deformation can lead to the fragmentation of the primary Al₃Zr phase and can promote the re-solution of Al₃Zr phase,which is very beneficial for the subsequent aging treatment.（6）The effect of extrusion ratio on the tissue properties of Al-1.0Zr alloy is discussed.The electrical conductivity and plasticity decrease with increasing extrusion ratio,and the tensile strength increases with increasing extrusion ratio.When the extrusion ratio is 30,the conductivity of the conductive rod is 48.38%IACS,the tensile strength is 185.6 MPa,and the elongation is 8.6%.In summary,the GAC technique can extend the solid solution of Zr in the aluminum matrix and is very beneficial for aging treatment.In addition,the GAC technology combines non-equilibrium solidification,in-line consolidation and extrusion,and can complete the preparation of wire rod products in one step operation with unlimited length,which is particularly suitable for the continuous preparation of Al-Zr alloy wire blanks and has unique advantages.